This invention relates generally to methods for coating metallic substrates and, more particularly, to methods for applying electrodepositable coatings onto an automotive substrate using a reverse coating process.
In the automotive industry, a conventional xe2x80x9creverse coating processxe2x80x9d consists of applying a primer coat by powder coating or powder electrodeposition coating onto an article, baking the coated article to effect the hardening of the coating, subjecting the remaining uncoated portion to a second electrodeposition and then baking the article again to effect hardening of the second coating. A topcoat, e.g. a basecoat and a clearcoat, is applied to at least the electrocoated outer surface of the substrate to provide acceptable aesthetics.
U.S. Pat. No. 4,333,807 discloses a different reverse coating process in which, after an initial resin powder primer coating is applied to the substrate, the resin powder is heated to a temperature sufficient to melt the coating but not to cure the coating, i.e., to cause a cross-linking reaction. The first coating is sanded and then an electrodeposition coating is applied, after which the coated substrate is heated to a temperature sufficient to cross-link both coatings.
U.S. Pat. No. 4,259,163 discloses yet another method of reverse coating a substrate. A binder resin and synthetic resin in the form of fine powder in an aqueous bath is electrodeposited upon the substrate. Next, an ionic synthetic resin is electrodeposited upon the area of the substrate not covered by the first electrodeposited coating, and then the coated substrate is baked to simultaneously harden both coatings.
In known reverse coating processes, a topcoat is applied over the reverse coated substrate, typically over at least the outer facing portion of the substrate, to provide the substrate with an aesthetically acceptable finish.
It would be advantageous to provide a reverse coating process that permits selectively coating, particularly electrocoating, selected areas of the substrate with a primer-surfacer.
An aspect of the present invention is a coated metallic article having a Class A surface and a non-Class A surface, the article comprising a primer-surfacer electrodeposited upon at least a portion of the Class A surface, and an anticorrosion material electrodeposited upon at least a portion of the non-Class A surface. The primer-surfacer comprises a polyurethane, polyester, or acrylic polymer material.
The present invention also provides a coated metallic article having a Class A surface and a non-Class A surface; the article comprising a primer-surfacer electrodeposited upon at least a portion of the Class A surface, and an anticorrosion material electrodeposited upon at least a portion of the non-Class A surface. The primer-surfacer is essentially free of powder material.
The present invention further provides a method of coating a metallic article having a Class A surface and a non-Class A surface, the method comprising electrodepositing a primer-surfacer upon at least a portion of the Class A surface, and electrodepositing an anticorrosion material upon at least a portion of the non-Class A surface. The primer-surfacer is essentially free of powder material and/or comprises a polyurethane, polyester, or acrylic polymer material.